Safety Factor and Inverse Reliability Measures

Probability performance measure and probability sufficiency factor are two inverse reliability measures that have gained importance as alternate measures of safety. Inverse measures have several advantages, including improving accuracy in response surface approximations, computational efficiency, and allowing easy estimates of resources needed for achieving the target safety levels. This paper establishes the relationship between the two inverse measures, and describes their advantages compared to the direct measures of probability and reliability index. Methods to compute the inverse measures are also described. Reliability based design optimization with inverse measure is demonstrated with a beam design example.